The New York senator raised more than $6 million in the first three months of the year, according to papers filed Thursday with the Federal Election Commission. The $2 million-a-month fundraising pace gave her $19.7 million cash on hand at the end of March for her reelection.

"It's mind-blowing. She is raising money at a presidential level," said Douglas Muzzio, a professor at Baruch College.

Clinton's two main challengers each reported far less as they vie for the GOP nomination.

Former Yonkers mayor John Spencer raised $1.1 million during the first quarter and Kathleen Troia "KT" McFarland, a former Reagan-era Pentagon official, about $200,000.

The Clinton campaign trumpeted how much of its money came from small, Internet-driven donations. More than 250,000 individuals donated to her 2006 campaign, and only one out of every 20 donations she received this quarter were larger than $100, the campaign said.